A Linux worm that spread in May 2001.
This worm was largely different from previous Linux worms like Ramen and Lion. It spread over network and cracked into vulnerable systems.
However, its basic goal was not to wreak havoc, but to fix security problems - to be specific, the vulnerability that Lion used to get in.
Most well-administered Linux systems don't have this sort of vulnerabilities (all exploits that Ramen and Lion needed were widely known and all people who care about security had patched their systems ages ago); however, systems administered by inexperienced admins may have been largely vulnerable.
The behavior of this worm reminds me of nanotechnology - sort of like "good worm" that multiplies and fixes all net problems. (Computer virus stuff is getting just as exciting as "real" microbiology =)
However, all worms still eat bandwidth and computing resources...